Multi-degree-of-freedom motion synchronous measurement system and method based on time-space domain information fusion

Abstract

The invention relates to a multi-degree-of-freedom motion synchronous measurement system and method based on time-space domain information fusion, which utilize a heterodyne interference phenomenon generated by a double-frequency light source to realize accurate measurement of displacement and angle by analyzing phase change of an interference signal generated by interaction of a measurement grating and a reference grating. The system comprises a double-frequency light source, an optical element, a measuring grating, a reference grating and a photoelectric detector, and the photoelectric detector comprises an array detector and a common photoelectric detector and is used for receiving interference light signals of different diffraction orders. The processing device at least comprises an angle measuring module. The angle module is used for resolving by fusing phase spatial-temporal characteristics and light spot displacement of signals on the array detector; a displacement module can be further included, calculation is carried out through the phase change of heterodyne interference signals on the detector along with time, and finally synchronous measurement of six-degree-of-freedom motion parameters can be achieved. The system has the advantages of being accurate, compact in size, high in light source efficiency and the like, and is suitable for multiple fields of photoetching machine wafer table positioning, ultra-precision machine tool machining and the like.

Description

Technical Field

[0001] The invention relates to a multi-degree-of-freedom precision measurement technology, and in particular to a multi-degree-of-freedom motion synchronous measurement system and method that integrates time-space domain information. Background Art

[0002] Multi-DOF precision measurement technology is the core foundation for supporting the high-end manufacturing field to move towards nano-level precision. In integrated circuit manufacturing, the six-DOF motion error (including X / Y / Z displacement and pitch / yaw / roll angle) of the lithography machine wafer stage needs to be strictly controlled at the sub-nanometer and sub-arc second level to ensure the consistency and yield of the chip line width. For example, in the extreme ultraviolet (EUV) lithography machine, if the angular yaw error generated by the wafer stage during high-speed scanning exceeds 0.1 arc second, it will directly cause the exposure pattern to be distorted, resulting in the risk of billions of dollars in chip scrapping. In the field of ultra-precision machine tools, the tools of the five-axis linkage machining center need to decouple the six-DOF posture error in real time. If there is inter-axis crosstalk in the angle measurement module (such as θX and θY coupling error), the shape accuracy deviation of the complex surface will exceed the permitted range. In the field of aerospace, the assembly of engine turbine blades requires simultaneous monitoring of millimeter-level displacement and micro-radian-level attitude angle deviation. The traditional single-DOF measurement method has become a bottleneck restricting assembly efficiency and reliability because it cannot achieve real-time decoupling of multi-dimensional errors.

[0003] Grating interferometer is regarded as a key technology to overcome the difficulty of six-degree-of-freedom measurement due to its ability to synchronously measure multi-dimensional parameters. Compared with the system complexity caused by laser interferometer's reliance on multi-path splicing, or the defect of capacitive sensor's measurement stroke being too small, grating interferometer can realize the coordinated solution of displacement and angle in a single optical path through the characteristics of diffracted light phase modulation. Its core advantages include: (1) sub-nanometer displacement resolution, through grating period subdivision and circuit signal processing, the resolution can reach 0.1nm; (2) multi-degree-of-freedom parallel measurement, using the ±1st order diffraction light interference effect of two-dimensional grating to synchronously capture X / Y / Z displacement and angle changes around three axes; (3) dynamic response characteristics, the modulation frequency of grating interferometer can reach MHz level, which is suitable for real-time feedback control of high-speed motion platform; (4) compact structure, a single reading head can cover multi-degree-of-freedom measurement, significantly reducing the complexity of system integration. However, the angle measurement module of the existing grating interferometer still has three major technical bottlenecks: first, the displacement and angle measurement units adopt a common optical path design, and incomplete spectral filtering leads to crosstalk between axes; second, the self-collimating angle module is sensitive to environmental vibrations, and tiny mechanical deformations will cause optical path misalignment; third, in order to achieve six-degree-of-freedom decoupling, a distributed layout of multiple reading heads is required, which leads to a surge in installation and adjustment costs and difficulty in synchronizing dynamic data.

[0004] The Lee team in South Korea first proposed a single-grating six-degree-of-freedom measurement system, which achieves X / Y / Z displacement and three-axis angle synchronous detection through single-grating diffraction light interference, with an angle error of <0.03 arc seconds. However, the system uses separate reference gratings and moving gratings, and the difference in the response of the dual optical paths to environmental temperature drift leads to insufficient dynamic measurement stability. The measured X-axis displacement error is as high as ±20nm, which is difficult to meet the positioning requirements of the lithography machine.

[0005] Gao's team at Tohoku University in Japan developed a dual-grating three-degree-of-freedom interferometer, which uses the diffraction light interference signal of the reference grating and the measurement grating to resolve the X / Y / Z displacement (resolution <1nm). Its innovation lies in the single measuring point design, but the Z-direction displacement range is limited by the spot movement effect (<1mm), and the angular error cannot be decoupled, and it is only suitable for micron-level error compensation of planar motion platforms. Gao's team further integrated the three-axis displacement sensor and the autocollimator to launch a multi-axis surface encoder, realizing six-degree-of-freedom measurement for the first time (angular resolution 0.1 arc seconds). However, its angle module relies on mechanical adjustment and alignment, resulting in a θX / θY error peak of ±0.5 arc seconds, and the sub-nanometer displacement accuracy requirements are not met (X / Y axis error ±6nm).

[0006] The Hsieh team in Taiwan proposed a heterodyne grating interferometer, which combines grating shearing with Michelson interference to increase the angular resolution to 0.05μrad (about 0.01 arc second). However, the system requires complex polarization optical components and high-precision lens groups, the Z-axis measurement range is limited to the focal length (<500μm), and the optical path stability is poor in dynamic environments.

[0007] Tohoku University in Japan proposed a three-reader surface encoder that can calculate six degrees of freedom through distributed measurement, with an angular resolution of 0.1 arc second. However, this method requires the polarization states of the three read heads to be strictly consistent, and dynamic data synchronization requires a dedicated high-speed calculation chip, which increases system cost and power consumption.

[0008] Lin Jie's team from Harbin Institute of Technology adopted a self-collimating incident light path design to expand the Z-direction displacement range to the millimeter level (resolution 4nm), but it only supports X / Y / Z three-degree-of-freedom measurement. The lack of an angle module makes it impossible to meet the requirements of six-degree-of-freedom scenarios.

[0009] The Tsinghua University team developed a dual-channel grating encoder that achieves six-DOF synchronous monitoring of dual components by sharing optical elements. Its innovation lies in the spatial multiplexing of the grating layout, but the measurement accuracy depends on the rigid connection of the subcomponents, and the grating engraving error will introduce cross-DOF coupling noise (the measured θZ crosstalk is up to 0.15 arc seconds).

[0010] The core contradiction of the current six-degree-of-freedom grating interferometer lies in the imbalance between the high-precision requirements of the angle measurement module and the system decoupling and environmental robustness. Specifically, it manifests itself as follows: (1) In the common optical path design, the displacement signal modulation and angle solution share the same optical path, and the residual reflection of the beam splitter causes the Z displacement noise to be mixed into the θX / Y signal (experimental verification of the crosstalk rate>5%); (2) The self-collimation angle module requires a long focal length lens group to improve sensitivity, but the difference in the thermal expansion coefficient of the lens amplifies the temperature drift error; (3) Although the multi-reader layout can improve decoupling, the grating line consistency is required to reach the sub-micron level, and the difference in data delay during dynamic measurement leads to a decrease in real-time performance. The above problems seriously restrict the large-scale application of grating interferometers in high-end equipment.

[0011] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0012] The main purpose of the present invention is to overcome the defects existing in the above-mentioned background technology and provide a multi-degree-of-freedom motion synchronous measurement system and method with time-space domain information fusion.

[0013] To achieve the above object, the present invention adopts the following technical solutions:

[0014] A multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion, comprising:

[0015] A dual-frequency light source comprises a first frequency laser (11) and a second frequency laser (12) that satisfy a beat frequency interference condition;

[0016] An optical element, used for adjusting the polarization state and performing beam separation and merging processing on the first frequency laser (11) and the second frequency laser (12);

[0017] A measuring grating (2) is fixed on a multi-dimensional motion platform and generates an interference signal as the platform moves;

[0018] A reference grating (3) is fixed and provides an interference reference;

[0019] Photodetectors, including:

[0020] A first array detector (40) is used to receive interference light signals of 0th order diffraction generated by the measuring grating and the reference grating, for measuring the X-axis angle and the Y-axis angle;

[0021] A second array detector (41) is used to receive a Z-axis angle measurement signal from an interference light signal of first-order diffraction in the X-direction generated by the measurement grating and the reference grating, for Z-axis angle measurement;

[0022] A processing device is configured to:

[0023] Utilizing the heterodyne interference phenomenon generated by the dual-frequency light source, analyzing phase changes of interference signals received by the first array detector (40) and the second array detector (41);

[0024] According to the phase change, analyzing the interference light signal of the 0th order diffraction received by the first array detector (40), and preliminarily calculating the rotation angle around the X-axis and the Y-axis according to the linear relationship between the phase difference and the rotation angle;

[0025] Analyzing the interference light signal of the first-order diffraction received by the second array detector (41) according to the phase change, and preliminarily calculating the rotation angle around the Z axis through the quadrant distribution difference caused by the light spot displacement;

[0026] The spatial distribution characteristics of the phase difference and the timing information of the spot displacement are integrated to jointly optimize the preliminary angle calculation results and output the precise rotation angles around the X, Y, and Z axes.

[0027] Furthermore, it also includes: a first common photodetector (42), a second common photodetector (43) and a third common photodetector (44);

[0028] The second array detector (41), the first ordinary photodetector (42), the second ordinary photodetector (43) and the third ordinary photodetector (44) are configured to receive interference light signals of positive first-order diffraction on the X-axis, interference light signals of positive first-order diffraction on the Y-axis, interference light signals of negative first-order diffraction on the X-axis and interference light signals of negative first-order diffraction on the Y-axis;

[0029] The processing device is further configured to:

[0030] By analyzing the four interference light signals received by the first ordinary photodetector (42), the second ordinary photodetector (43), the third ordinary photodetector (44) and the second array detector (41), and combining the interference signal of the 0th order diffraction of the first array detector (40), the displacement along the X, Y and Z directions is calculated;

[0031] Phase differential technology is used to eliminate the coupling interference of Z-axis displacement on X / Y direction solution, and a displacement solution model is constructed;

[0032] In general, the XYZ linear displacement and XYZ angular displacement measurements are achieved through the five-way interference signal (5) on the detector.

[0033] Thus, the synchronous measurement of six-degree-of-freedom motion parameters is achieved.

[0034] A multi-degree-of-freedom motion synchronous measurement method with time-space domain information fusion uses the multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion to perform multi-degree-of-freedom motion synchronous measurement.

[0035] The present invention has the following beneficial effects:

[0036] The present invention proposes a multi-degree-of-freedom motion synchronous measurement system and method with time-space information fusion, which innovatively integrates time-space information and realizes the synchronous measurement of multi-degree-of-freedom motion. The present invention not only expands the measurement dimension of the traditional planar grating interferometer from three degrees of freedom to six degrees of freedom, but also significantly improves the measurement accuracy and reliability by integrating the time-space information difference of the heterodyne interference wavefront into the measurement principle.

[0037] The multi-degree-of-freedom motion synchronous measurement system and method may include two parts: angle measurement and displacement measurement. Displacement measurement is determined by heterodyne interference phase change, and angle measurement uses the 0th order and one of the 1st order diffracted light. As the three-degree-of-freedom angle of the measuring grating changes, the angle is solved by the time phase difference at a fixed position. The present invention has the advantages of accurate model, compact size, and high light source efficiency, which greatly promotes the rapid development of high-end equipment such as lithography machines, coordinate measuring machines, and high-end CNC machine tools, and accelerates the development of large-scale atomic manufacturing technology.

[0038] The present invention achieves high-precision decoupling of six degrees of freedom under a single reading head architecture through optical path reconstruction and signal decoupling algorithm innovation, while also having both environmental interference resistance and engineering economy. This design not only solves the imbalance problem between the high-precision requirements of the angle measurement module of the existing grating interferometer and the system decoupling and environmental robustness, but also eliminates the coupling interference of the Z-axis displacement on the X / Y direction solution, builds a displacement solution model, and realizes the synchronous measurement of the six-degree-of-freedom motion parameters.

[0039] The remarkable technical effect of the present invention is that it can achieve sub-nanometer precision six-degree-of-freedom synchronous measurement, is easy to miniaturize, and the theoretical minimum size can reach within 100mm*100mm*50mm, and the error level is low. The quasi-common optical path method is adopted to reduce the influence of spatial refractive index and light source frequency fluctuations, thereby improving the stability and accuracy of the measurement. These technical advantages make the present invention have broad application prospects in high-end manufacturing fields such as lithography machine wafer stage positioning, ultra-precision machine tool processing, atomic force microscope, atomic-level manufacturing probe, etc.

[0040] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 2 is a diagram of the overall optical path structure of an embodiment of the present invention.

[0042] Figure 2 This is a distribution diagram of the angle measurement modules according to an embodiment of the present invention.

[0043] Figure 3 Schematic diagram of the XY angle measurement principle (XOZ plane) of an embodiment of the present invention.

[0044] Figure 4 Schematic diagram of the XY angle measurement principle (XOY plane) of an embodiment of the present invention.

[0045] Figure 5 Schematic diagram of the Z angle measurement principle of an embodiment of the present invention.

[0046] FIG. 6A to FIG. 6E The following are experimental results of the embodiments of the present invention under five typical situations.

[0047] Reference numerals:

[0048] 1. Dual-frequency laser light source, 2. Measuring grating, 3. Reference grating, 4. Photodetector, 5. Heterodyne interference signal, 11. Laser f1, 12. Laser f2, 21. First half-wave plate, 22. First polarizer, 23. First polarization beam splitter, 24. First quarter-wave plate, 25. Second half-wave plate, 26. Third half-wave plate, 27. Second polarizer, 28. Second polarization beam splitter, 29. Second quarter-wave plate, 30. Third polarizer, 40. First array detector, 41. Second array detector, 42. First ordinary photodetector, 43. Second ordinary photodetector, 44. Third ordinary photodetector. DETAILED DESCRIPTION

[0049] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0050] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for fixing as well as for coupling or communication.

[0051] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0052] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0053] See also Figure 1 and Figure 2 The embodiment of the present invention provides a multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion, including: a dual-frequency light source, including a first frequency laser 11 and a second frequency laser 12 that meet the beat frequency interference condition; an optical element, used to adjust the polarization state and separate and merge the beams of the first frequency laser 11 and the second frequency laser 12; a measuring grating 2, fixed on a multi-dimensional motion platform, generating an interference signal as the platform moves; a reference grating 3, fixed and stationary, providing an interference reference; a photoelectric detector, including: a first array detector 40, used to receive the interference light signal of the 0th order diffraction generated by the measuring grating 2 and the reference grating 3, for measuring the X-axis angle and the Y-axis angle; a second array detector 41, used to receive the X-direction interference light signal of the 1st order diffraction generated by the measuring grating 2 and the reference grating 3, for measuring the Z-axis angle; an angle module of a processing device The block is solved by fusing the phase space-time characteristics and the spot displacement of the signal on the array detector. Specifically, the processing device is configured to: use the heterodyne interference phenomenon generated by the dual-frequency light source to analyze the phase change of the interference signal received by the first array detector 40 and the second array detector 41; according to the phase change, analyze the interference light signal of the 0th order diffraction received by the first array detector 40, and preliminarily calculate the rotation angle around the X-axis and the Y-axis according to the linear relationship between the phase difference and the rotation angle; according to the phase change, analyze the interference light signal of the 1st order diffraction received by the second array detector 41, and preliminarily calculate the rotation angle around the Z-axis through the quadrant distribution difference caused by the spot displacement; fuse the spatial distribution characteristics of the phase difference with the timing information of the spot displacement, jointly optimize the preliminary angle calculation results, and output the precise rotation angles around the X, Y, and Z axes.

[0054] like Figure 1 to Figure 2As shown, in a preferred embodiment, the system further includes: a first ordinary photodetector 42, a second ordinary photodetector 43 and a third ordinary photodetector 44; the second array detector 41, the first ordinary photodetector 42, the second ordinary photodetector 43 and the third ordinary photodetector 44 are configured to receive the interference light signal of the first-order diffraction of the positive X-axis, the interference light signal of the first-order diffraction of the positive Y-axis, the interference light signal of the first-order diffraction of the negative X-axis and the interference light signal of the first-order diffraction of the negative Y-axis; the displacement module of the processing device detects Specifically, the processing device is further configured to: analyze the four-way interference light signals received by the first ordinary photodetector 42, the second ordinary photodetector 43, the third ordinary photodetector 44 and the second array detector 41, and combine the interference signal of the 0th order diffraction of the first array detector 40 to solve the displacement along the X, Y and Z directions; use the phase difference technology to eliminate the coupling interference of the Z-axis displacement on the X / Y direction solution, and construct a displacement solution model; thereby, realize the synchronous measurement of the six-degree-of-freedom motion parameters.

[0055] like Figure 1 to Figure 2As shown, in a preferred embodiment, the optical elements include: a first half-wave plate 21, a first polarizer 22, a first polarization beam splitter prism 23, a first quarter-wave plate 24, a second half-wave plate 25, a third half-wave plate 26, a second polarizer 27, a second polarization beam splitter prism 28, a second quarter-wave plate 29, and a third polarizer 30; wherein the first frequency laser 11 is adjusted to p-polarized light by the first half-wave plate 21 and the first polarizer 22 in sequence, enters the first polarization beam splitter prism 23, and is further converted into circularly polarized light by the first quarter-wave plate, and finally incident on the measuring grating 2; the five diffracted light beams generated by the measuring grating 2 are converted into s-polarized light after passing through the first quarter-wave plate 24, and are reflected to the beam combining path through the first polarization beam splitter prism 23; the reflected s-polarized light is converted into p-polarized light by the second half-wave plate 25, and is transmitted through the second polarization beam splitter prism 28 To the third polarizer 30, divided into equal p-polarized light and s-polarized light; wherein, the second frequency laser 12 is adjusted to p-polarized light through the third half-wave plate 26 and the second polarizer 27 in sequence, enters the second polarization beam splitter prism 28, and is further converted into circularly polarized light through the second quarter-wave plate, and finally incident on the reference grating 3; the five diffracted light beams generated by the reference grating 3 are converted into s-polarized light after the polarization state passes through the second quarter-wave plate 29, and are reflected to the beam combining path through the second polarization beam splitter prism 28; the reflected s-polarized light is divided into equal p-polarized light and s-polarized light through the third polarizer 30; and then interferes with the first frequency laser 11 to form five interference signals 5, which are respectively received by the first array detector 40, the second array detector 41, the first ordinary photodetector 42, the second ordinary photodetector 43, and the third ordinary photodetector 44 in the photodetector 4.

[0056] In some embodiments, the measurement grating 2 and the reference grating 3 are both two-dimensional reflective diffraction gratings.

[0057] In some embodiments, when calculating the displacement along the X, Y, and Z directions, the processing device is further configured to: extract the phase term related to the displacement in each signal based on the phase change of the five interference signals; automatically compensate for the optical path difference in the X / Y direction through a symmetrical optical path layout, and use phase difference technology to eliminate the coupling interference of the Z-axis displacement on the X / Y direction displacement solution; construct a displacement solution model based on the differential relationship of the phase term, separate the displacement components in the X / Y / Z directions, and realize three-dimensional displacement measurement through the joint solution of multiple signals.

[0058] In some embodiments, when calculating the rotation angles around the X-axis and the Y-axis, the processing device is further configured to: analyze the spatial distribution of the phase difference of each detection point through the 0-order interference light signal received by the first array detector 40, and identify the linear change gradient of the phase difference along the X-axis or the Y-axis; establish a mathematical model of the rotation angle and the phase difference change rate according to the linear gradient direction and the phase difference difference between adjacent detection points, combined with the frequency parameters of the dual-frequency light source and the speed of light; separate the rotation angle components around the X-axis and the Y-axis by solving the mathematical model, and output the accurate rotation angles around the X-axis and the Y-axis based on the fusion of time and space domain information.

[0059] In some embodiments, when calculating the rotation angle around the Z axis, the processing device is further configured to: analyze the difference in quadrant distribution of the interference area caused by the light spot displacement through the first-order diffraction light signal received by the second array detector 41; establish a mathematical model of the rotation angle and the quadrant signal difference based on the geometric relationship between the light spot center offset and the rotation angle; correct the photoelectric conversion error and algorithm nonlinearity by calibrating the system constants, perform angle calculation in combination with the light spot position information, and output the precise rotation angle around the Z axis.

[0060] The embodiment of the present invention also provides a method for synchronously measuring multi-degree-of-freedom motion by fusion of time-space domain information, and uses the synchronously measuring multi-degree-of-freedom motion by fusion of time-space domain information described in any of the above embodiments to perform synchronous measurement of multi-degree-of-freedom motion.

[0061] The specific embodiments and experimental verification of the present invention are further described below.

[0062] Six degrees of freedom measurement of the overall optical path:

[0063] This solution uses a dual-frequency light source, two two-dimensional reflective diffraction gratings, detectors, and optical components to achieve six-degree-of-freedom measurement. The dual-frequency light source used needs to have two separable laser heads that can output lasers with a certain frequency difference. The detector includes 5 photodetectors. Its structure is as follows Figure 1 The coordinate system is set as shown in Figure 1 As shown, the direction perpendicular to the measured grating surface is the Z direction, and the X and Y directions are orthogonal within the measured grating surface. The X direction is the horizontal direction, and the Y direction is the vertical direction. The corresponding rotation angle R around the X, Y, and Z axes x , R y , R z Defined by the right-hand screw rule.

[0064] like Figure 1As shown, the frequency difference between the first laser beam 11 and the second laser beam 12 is f0=f1-f2 (the frequencies of f1 and f2 are close, and the difference between the two is much smaller than the frequencies of the two themselves, thus satisfying the basic condition of beat frequency interference). The first laser beam 11 enters the first polarization beam splitter prism 23 after passing through the first half-wave plate 21 and the first polarizer 22, and the second laser beam 12 enters the second polarization beam splitter prism 28 after passing through the third half-wave plate 26 and the second polarizer 27.

[0065] Then, each laser beam is incident on the corresponding grating (period 1000nm, 2D reflective grating): the first laser beam 11 interacts with the measurement grating 2, and the second laser beam 12 interacts with the reference grating 3. Each grating diffracts the incident light into five beams, namely: zero-order diffraction light, first-order diffraction light (positive direction of the X-axis), first-order diffraction light (negative direction of the X-axis), first-order diffraction light (positive direction of the Y-axis) and first-order diffraction light (negative direction of the Y-axis). Finally, the ten diffracted light beams pass through other components (including polarization beam splitter, half-wave plate, quarter-wave plate and polarizer) and interfere on the photodetector (PD) 4, generating five beat frequency (or heterodyne) interference signals, which are received by the first array detector 40, the second array detector 41, the first ordinary photodetector 42, the second ordinary photodetector 43, and the third ordinary photodetector 44 respectively.

[0066] Next, the polarization state of the light beam is analyzed. First, for the first laser beam 11, after passing through the first half-wave plate 21 and the first polarizer 22, it becomes p-polarized light. Then it passes through the first polarization beam splitter prism 23, and after passing through the first quarter-wave plate 24, it is converted into circularly polarized light. This beam is then reflected and diffracted at the diffraction grating 2. The five output beams are reflected back through the first quarter-wave plate 24 and become s-polarized light. Therefore, the light beam is reflected at the first polarization beam splitter prism 23, passes through the second half-wave plate 25, and is converted into p-polarized light, and then passes through the second polarization beam splitter prism 28. After passing through the third polarizer 30, it is divided into equal p-polarized light and s-polarized light. Next, we analyze the second laser beam 12. This light beam also passes through the third half-wave plate 26, the second polarizer 27, the second polarization beam splitter prism 28, the second quarter-wave plate 29, and then passes through the second quarter-wave plate 29, the second polarization beam splitter prism 28 and the third polarizer 30 after being reflected and diffracted on the reference grating 3. After passing through the third polarizer 30, the light beam is divided into equal p-polarized light and s-polarized light, and then interferes with the first laser beam 11 to form five interference signals (0, X +1 , X -1 , Y +1 and Y -1 ), are received by the first array detector 40, the second array detector 41, the first ordinary photodetector 42, the second ordinary photodetector 43, and the third ordinary photodetector 44 respectively.

[0067] In general, a symmetrical optical path architecture is established. Based on the polarization beam splitter (PBS) and the double grating (G 1 ,G 2 ) to construct a spatially symmetrical interference system, such as Figure 1 As shown. Dual frequency laser (f 1 ,f 2 ) The orthogonal polarization states are split by PBS to form the measurement / reference optical path:

[0068]

[0069] Three-degree-of-freedom linear displacement measurement method:

[0070] The three-degree-of-freedom linear displacement measurement method requires five detectors, which require the following signals: I 0 (the signal in the first quadrant from the first array detector 40), (the signal in the first quadrant from the second array detector 41), (the signal from the second ordinary photodetector 43), (the signal from the first common photodetector 42), (Signal from the third ordinary photodetector 44)

[0071] The diffraction angle θ d Satisfies the grating equation g sinθ d =λ, g is the grating period. Symmetrical layout is used to achieve automatic compensation of the optical path in X / Y direction. Five interference signals I 0 (the signal in the first quadrant from the first array detector 40), (the signal in the first quadrant from the second array detector 41), (the signal from the second ordinary photodetector 43), (the signal from the first common photodetector 42), (Signal from the third common photodetector 44) solves the grating XYZ displacement, and the signal expression is:

[0072] I i ∝U i cos(2πf 0 t+Φ i +D i )(2)

[0073] The displacement phase term Φ i satisfy:

[0074] Φ 0 =4πnz / λ

[0075]

[0076] By eliminating the Z-axis coupling term through phase difference, the displacement solution model is obtained:

[0077]

[0078] Three-degree-of-freedom angular displacement measurement method:

[0079] The three-degree-of-freedom angular displacement measurement method requires two detectors, which require the following signals: I 0 (signals from all quadrants of the first array detector 40), (Signals from all quadrants of the second array detector 41).

[0080] The three-degree-of-freedom angular displacement measurement method consists of two parts, such as Figure 2 As shown, the 0th order interference light is hit on the first array detector 40 for XY angle measurement (time-space information fusion), and the 1st order diffraction light is hit on the second array detector 41 for Z angle measurement (intensity distribution), which will be introduced one by one below.

[0081] XY angular displacement measurement method:

[0082] like Figure 3 As shown, when the two beam frequencies are f 1 and f 2 When the first laser beam 11 and the second laser beam 12 pass through multiple elements and vertically enter the detector 4, the initial phase difference is uniformly distributed in space. 1 After the beam of the first frequency laser 11 rotates about y by θ, its wave vector obtains a transverse component k 1x ≈k 1 θ, and the frequency is f 2 The light beam of the second frequency laser 12 still propagates along z. At this time, the phase difference between the two light beams at the plane z=0 of the detector 4 is:

[0083]

[0084] Where x is the position coordinate of the detector 4 in the x direction, and c is the speed of light. Phase difference and rotation angle θ, frequency f 1 is proportional to the position x. Similarly, if the rotation occurs along the x-axis, the phase difference will depend on the y-coordinate:

[0085]

[0086] Initial state: The wave vectors of the two light beams are both along the z-axis, the phase difference at each point of the detector is constant, and there is no spatial change.

[0087] Wave vector decomposition after rotation: f 1The beam rotates θ around the y-axis, and the transverse component of the wave vector is k 1x =k 1 sinθ≈k 1 θ, longitudinal component k 1z ≈k 1 cosθ≈k 1 3. Phase difference calculation: The phase difference between the two beams of light at point (x, y) is:

[0088] Δφ=(k 1 -k 2 )·r=k 1x x=k 1 θx

[0089] Substitute k 1 =2πf 1 / c, we get:

[0090]

[0091] The phase difference varies linearly with the position of the detector, and the proportionality coefficient is determined by the rotation angle θ and the frequency f 1 The relationship between the phase difference at position (x, y) on the array detector and the rotation angle θ is:

[0092]

[0093] The specific rotation direction depends on the rotation direction (about the y-axis or the x-axis). The phase difference is proportional to the rotation angle θ and the frequency f 1 and horizontal position coordinates.

[0094] like Figure 4 As shown, consider a 3×3 array detector, the distance between adjacent points is T, the coordinate system takes the center point as the origin (0,0), and the position of each point is (x,y) = (±T,±T). When the first frequency laser 11 rotates slightly relative to the second frequency laser 12, the relationship between the phase difference and the rotation angle is as follows:

[0095] 1. Rotate in the x direction (rotate θ around the x axis) x )

[0096] Wave vector change: k 1 In the x direction there is a component k 1x =k 1 sinθ x ≈k 1 θ x . Phase difference formula:

[0097]

[0098] Calculate the rotation angle θ x : Using the phase difference between adjacent x-direction points (e.g. x=T and x=-T):

[0099]

[0100] 2. Rotate in the y direction (rotate θ around the y axis) y )

[0101] Wave vector change: k 1 In the y direction there is a component k 1y =k 1 sinθ y ≈k 1 θ y . Phase difference formula:

[0102]

[0103] Calculate the rotation angle θ y : Using the phase difference between adjacent points in the y direction (e.g. y=T and y=-T):

[0104]

[0105] Z angular displacement measurement method:

[0106] like Figure 5 As shown in the figure, this module introduces the y-direction spot displacement by rotating the laser beam, and realizes angle resolution by combining the signal difference between different quadrants of the array detector. When f1 rotates around point (m, 0) (m> spot diameter) by θ, its spot center produces a y-direction displacement Δy on the plane of the array detector, and the area distribution of the upper and lower quadrants of the interference region changes with Δy. By establishing a mathematical model of Δy and θ and the relationship between the quadrant area ratio, the rotation angle is output in real time. The formula is derived as follows:

[0107] 1. Spot displacement model

[0108] After f1 rotates around (m, 0) by an angle θ, the y-direction offset Δy of the center of the light spot in the array detector plane is determined by the geometric relationship:

[0109] Δy=mtanθ≈mθ

[0110] 2. Interference area quadrant distribution

[0111] Assume the spot radius r, and the y-direction distance between the two spot centers is d=Δy. The total area A of the intersection region is:

[0112]

[0113] The difference in area between the upper and lower quadrants is obtained from symmetry:

[0114] ΔA=A upper -A lower =K·d=Kmθ

[0115] Where K is a proportionality factor related to the spot radius and the detector sensitivity, which is determined by calibration.

[0116] 3. Signal analysis angle

[0117] The signal difference between the upper and lower halves of the array detector (the difference between Q1+Q2 and Q3+Q4) is proportional to ΔA:

[0118]

[0119] Q1, Q2, Q3, Q4 are the signal intensities of the four quadrants of the second array detector 41; K' is the system calibration constant, including the photoelectric conversion and algorithm correction factors; m is the geometric distance from the 0th order diffraction light interference signal to the 1st order diffraction light interference signal in the X-direction.

[0120] Table 1 Summary of angle measurement formulas

[0121]

[0122] Feasibility verification of angle measurement:

[0123] (1) Physical verification

[0124] 1. x / y direction independence: The phase difference depends only on the coordinates of the corresponding direction and has nothing to do with the other direction.

[0125] 2. Composition in z direction: The rotation around the z axis can be decomposed into the coupling effects in the x and y directions, and the total rotation angle is the geometric synthesis of the two.

[0126] 3. Resolution limitation: The sensitivity of angle detection is positively correlated with the laser frequency and the detector spacing. High-frequency lasers or large-spacing detectors can improve the angle resolution.

[0127] Conclusion: By measuring the phase difference distribution on the array detector, the rotation angles in the x and y directions can be uniquely determined, and the total rotation angle around the z axis can be obtained by plane fitting.

[0128] (2) Experimental verification

[0129] To verify the feasibility of this solution, the phase difference distribution of a 10×10 array detector under different deflection conditions was simulated (experimental parameters: f1=10e14Hz, T=1mm). The following are the experimental results of five typical cases:

[0130] Case 1: No deflection (θx=0,θy=0)

[0131] Phase distribution: uniform phase difference across the entire plane ( Fig. 6A ), the color map is a single hue, indicating no spatial gradient.

[0132] Technical significance: Verify the system benchmark status, eliminate environmental noise interference, and ensure the stability of the detection zero point.

[0133] Case 2: Single axis deflection (θx=0.01rad,θy=0)

[0134] Phase distribution: The phase difference increases linearly along the x-axis ( Figure 6B ), there is no change in the y direction, and the color appears as horizontal stripes.

[0135] Technical significance: Verify the system's ability to detect deflection in a single direction. The phase gradient slope is proportional to the deflection angle, which conforms to the formula

[0136] Case 3: Single axis deflection (θx=0,θy=0.01rad)

[0137] Phase distribution: The phase difference increases linearly along the y-axis ( Figure 6C ), the colors appear in vertical stripes, forming an orthogonal pattern with case 4.

[0138] Technical significance: It is demonstrated that the system can independently detect deflection in the x and y directions and is suitable for multi-DOF motion monitoring.

[0139] Case 4: Compound deflection (θx=0.02rad,θy=0.01rad)

[0140] Phase distribution: The phase difference is superimposed along the x and y directions to form a diagonal gradient ( Fig.6D ), the color transitions continuously from blue (negative phase) to red (positive phase).

[0141] Technical significance: It proves that the system can detect compound angle deflection, and the phase gradient direction is linearly related to the deflection direction, which meets the requirements of angle vector decomposition.

[0142] Case 5: Compound deflection (θx=0.01rad,θy=0.02rad)

[0143] Phase distribution: The phase gradient direction is orthogonal to that in case 4 ( Fig. 6E ), verifying the one-to-one correspondence between the angle direction and the phase gradient direction.

[0144] Technical significance: By comparing the phase patterns of different compound deflections, the system can uniquely determine the deflection angle vector and avoid the problem of multiple solutions.

[0145] In addition, adding an array detector at the first-order diffracted light can achieve incremental measurement in the z-direction.

[0146] In summary, the present invention proposes a multi-degree-of-freedom motion synchronous measurement system and method based on grating interferometry, which integrates time and space domain information and realizes high-precision angle and displacement measurement. Through the innovation of optical path reconstruction and signal decoupling algorithm, the present invention can realize high-precision decoupling of six degrees of freedom under a single reading head architecture, while having good environmental interference resistance and engineering economy.

[0147] The core contribution of the present invention is to realize angle measurement by using the method of space-time domain fusion. The inventor discovered and demonstrated that the space-time information under heterodyne interference is a natural phenomenon, and integrated it to establish a set of explainable mechanisms for measuring angles. Furthermore, the angle measurement scheme is combined with the three-degree-of-freedom displacement measurement system to form a complete six-degree-of-freedom motion measurement scheme, which includes an optical path structure design and a six-degree-of-freedom solution model. The six-degree-of-freedom measurement scheme includes two parts: displacement measurement and angle measurement. Displacement measurement is achieved through heterodyne interference phase change. The interference signal comes from the reference two-dimensional grating in the reading head and the 0th and 1st order diffraction of the measurement two-dimensional grating fixed on the multi-dimensional motion platform, a total of 5 beams of photosynthetic light. Angle measurement uses the 0th order and one of the 1st order diffracted light. As the three-degree-of-freedom angle of the measuring grating changes, the angle is solved by the time phase difference at a fixed position.

[0148] The technical effects of the present invention are remarkable, including:

[0149] Achieve six-degree-of-freedom synchronous measurement with sub-nanometer accuracy by using a three-way array detector plus a five-way interference signal joint solution.

[0150] It is easy to achieve miniaturization, and the theoretical minimum size can be within 100mm*100mm*50mm.

[0151] The error level is low, and the quasi-common optical path method is adopted to reduce the influence of spatial refractive index and light source frequency fluctuations.

[0152] The six-degree-of-freedom motion synchronous measurement solution of the present invention has the advantages of accurate model, compact size, high light source efficiency, etc., and can be widely used in the fields of lithography wafer stage positioning, ultra-precision machine tool processing, atomic force microscope, atomic-level manufacturing probe, etc. This will greatly promote the rapid development of high-end equipment such as lithography machines, coordinate measuring machines, high-end CNC machine tools, and accelerate the development of large-scale atomic manufacturing technology.

[0153] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A multi-degree-of-freedom motion synchronous measurement system with time-space information fusion, characterized in that: include: A dual-frequency light source comprises a first frequency laser (11) and a second frequency laser (12) that satisfy a beat frequency interference condition; An optical element, used for adjusting the polarization state and performing beam separation and merging processing on the first frequency laser (11) and the second frequency laser (12); A measuring grating (2) is fixed on a multi-dimensional motion platform and generates an interference signal as the platform moves; A reference grating (3) is fixed and provides an interference reference; Photodetectors, including: A first array detector (40) is used to receive interference light signals of 0th order diffraction generated by the measuring grating and the reference grating, for measuring the X-axis angle and the Y-axis angle; The second array detector (41) is used to receive the interference light signal of the first-order diffraction in the X direction generated by the measuring grating and the reference grating, for Z-axis angle measurement; the processing device is configured as follows: Utilizing the heterodyne interference phenomenon generated by the dual-frequency light source, analyzing phase changes of interference signals received by the first array detector (40) and the second array detector (41); According to the phase change, analyzing the interference light signal of the 0th order diffraction received by the first array detector (40), and preliminarily calculating the rotation angle around the X-axis and the Y-axis according to the linear relationship between the phase difference and the rotation angle; Analyzing the interference light signal of the first-order diffraction received by the second array detector (41) according to the phase change, and preliminarily calculating the rotation angle around the Z axis through the quadrant distribution difference caused by the light spot displacement; The spatial distribution characteristics of the phase difference and the timing information of the spot displacement are integrated to jointly optimize the preliminary angle calculation results and output the precise rotation angles around the X, Y, and Z axes.

2. The multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion according to claim 1 is characterized in that: Also includes: A first common photodetector (42), a second common photodetector (43) and a third common photodetector (44); The second array detector (41), the first ordinary photodetector (42), the second ordinary photodetector (43) and the third ordinary photodetector (44) are configured to receive interference light signals of positive first-order diffraction on the X-axis, interference light signals of positive first-order diffraction on the Y-axis, interference light signals of negative first-order diffraction on the X-axis and interference light signals of negative first-order diffraction on the Y-axis; The processing device is further configured to: By analyzing the four interference light signals received by the first ordinary photodetector (42), the second ordinary photodetector (43), the third ordinary photodetector (44) and the second array detector (41), and combining the interference signal of the 0th order diffraction of the first array detector (40), the displacement along the X, Y and Z directions is calculated; Phase differential technology is used to eliminate the coupling interference of Z-axis displacement on X / Y direction solution, and a displacement solution model is constructed; Thus, the synchronous measurement of six-degree-of-freedom motion parameters is achieved.

3. The multi-degree-of-freedom motion synchronous measurement system with spatiotemporal information fusion according to claim 2 is characterized in that: The optical element comprises: A first half-wave plate (21), a first polarizer (22), a first polarization beam splitter prism (23), a first quarter-wave plate (24), a second half-wave plate (25), a third half-wave plate (26), a second polarizer (27), a second polarization beam splitter prism (28), a second quarter-wave plate (29), and a third polarizer (30); The first frequency laser (11) is adjusted to p-polarized light through the first half-wave plate (21) and the first polarizer (22) in sequence, enters the first polarization beam splitter prism (23), and is further converted into circularly polarized light through the first quarter-wave plate, and finally incident on the measuring grating (2); the polarization state of the five diffracted lights generated by the measuring grating (2) is converted into s-polarized light after passing through the first quarter-wave plate (24), and is reflected to the beam combining path through the first polarization beam splitter prism (23); the reflected s-polarized light is converted into p-polarized light through the second half-wave plate (25), and is transmitted to the third polarizer (30) through the second polarization beam splitter prism (28), and is divided into equal p-polarized light and s-polarized light; The second frequency laser (12) is adjusted to p-polarized light by passing through a third half-wave plate (26) and a second polarizer (27) in sequence, enters a second polarization beam splitter prism (28), and is further converted into circularly polarized light by passing through a second quarter-wave plate, and finally incident on a reference grating (3); the five diffracted lights generated by the reference grating (3) are converted into s-polarized light by passing through a second quarter-wave plate (29), and are reflected to a beam combining path by the second polarization beam splitter prism (28); the reflected s-polarized light is divided into equal p-polarized light and s-polarized light by passing through a third polarizer (30); and then interferes with the first frequency laser (11) to form five interference signals (5), which are respectively received by a first array detector (40), a second array detector (41), a first ordinary photodetector (42), a second ordinary photodetector (43), and a third ordinary photodetector (44) in a photodetector (4).

4. The multi-degree-of-freedom motion synchronous measurement system with spatiotemporal information fusion according to claim 1 is characterized in that: The measuring grating and the reference grating are both two-dimensional reflective diffraction gratings.

5. The multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion according to claim 3 is characterized in that: When calculating the displacement along the X, Y, and Z directions, the processing device is further configured as follows: Based on the phase changes of the five interference signals, the phase terms related to the displacement in each signal are extracted; Symmetrical optical path layout is used to automatically compensate for the optical path difference in the X / Y direction, and phase difference technology is used to eliminate the coupling interference of Z-axis displacement on X / Y direction displacement solution; A displacement calculation model is constructed according to the differential relationship of the phase terms, the displacement components in the X / Y / Z directions are separated, and three-dimensional displacement measurement is achieved through the joint calculation of multi-channel signals.

6. The multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion according to claim 1 is characterized in that: When calculating the rotation angles around the X-axis and the Y-axis, the processing device is further configured to: Analyzing the spatial distribution of the phase difference at each detection point through the 0th order interference light signal received by the first array detector (40), and identifying the linear variation gradient of the phase difference along the X-axis or the Y-axis; According to the linear gradient direction and the phase difference difference between adjacent detection points, combined with the frequency parameters and light speed of the dual-frequency light source, a mathematical model of the rotation angle and the phase difference change rate is established; By solving the mathematical model, the rotation angle components around the X-axis and the Y-axis are separated, and based on the spatiotemporal information fusion, the accurate rotation angles around the X-axis and the Y-axis are output.

7. The multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion according to claim 1 is characterized in that: When calculating the rotation angle around the Z axis, the processing device is further configured to: Analyzing the difference in quadrant distribution of the interference region caused by the light spot displacement through the first-order diffraction light signal received by the second array detector (41); According to the geometric relationship between the center offset of the light spot and the rotation angle, a mathematical model of the rotation angle and the quadrant signal difference is established; The photoelectric conversion error and algorithm nonlinearity are corrected by calibrating the system constants, and the angle is calculated based on the spot position information to output the precise rotation angle around the Z axis.

8. The multi-degree-of-freedom motion synchronous measurement system with time-space domain information fusion according to claim 1 is characterized in that: The mathematical model for calculating the rotation angles around the X, Y, and Z axes by the processing device specifically includes: Rotate angle θ around the X axis x The calculation formula is: Wherein, Δφ is the phase difference caused by rotation around the X-axis; c is the speed of light; f1 is the frequency of the first-frequency laser; T is the spacing between adjacent detection points in the array detector; Rotate angle θ around the Y axis y The calculation formula is: Where Δφ is the phase difference caused by rotation around the Y axis; Rotation angle θ around the Z axis z The calculation formula is: Among them, Q1, Q2, Q3, Q4 are the signal intensities of the four quadrants of the second array detector (41); K' is a system calibration constant, including photoelectric conversion and algorithm correction factors; and m is the geometric distance from the 0th order diffraction light interference signal to the 1st order diffraction light interference signal in the X-direction.

9. A multi-degree-of-freedom motion synchronous measurement method with spatiotemporal information fusion, characterized in that: Multi-degree-of-freedom motion synchronous measurement is performed using the multi-degree-of-freedom motion synchronous measurement system according to the spatiotemporal information fusion according to any one of claims 1 to 8.

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